I'm divided about this.
Whilst it would be amazing to have an MMO where you can customize your own character and explore the entire Narutoverse, the actual product may not be exactly what we've dreamt about.
It would take a lot of time and work to pull it off correctly, considering that the slightest error could lose tons of fans/players.
Combat would be another issue. Unless they could integrate a fighting system like the Storm series has, it would just be a standard MMO turn-based combat. Not only does that become boring at times, but it doesn't really suit Naruto. Fights should be fast and action packed, and I don't see how an MMO could do that. It would essentially be two games in one, and most companies would probably avoid it.